Strange Custom Rear End

Okay, I am starting to accumulate the performance parts for my 72 Fury. Going to have a 700 plus hp 505. Not needing a drag car/but a respectable street car. Am talking with Strange about a custom S60 rear end. I have some ideas, but want to hear from the collective reasoning of the group.

1. Final Ratio?
2. Housing Dimension (not sure why Strange is asking this, and I do not know the answer)
3. Perch Location (I don't know why Strange is asking, but I am using the current stock spring location)

Okay, I am starting to accumulate the performance parts for my 72 Fury. Going to have a 700 plus hp 505. Not needing a drag car/but a respectable street car. Am talking with Strange about a custom S60 rear end. I have some ideas, but want to hear from the collective reasoning of the group.

1. Final Ratio?
2. Housing Dimension (not sure why Strange is asking this, and I do not know the answer)
3. Perch Location (I don't know why Strange is asking, but I am using the current stock spring location)

Thanks for the help and advice!

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1. A 3.55 is popular for a performance street car. Keeps RPM down & still enhances lower end grunt. Your torque curve can affect this too. Very easy to move the torque up too high for a heavy street car.
2. If you are not Mini tubbing then measure the flange to flange on the rear you have now. So that way the same wheels & tires will fit. See A below.
3. Again if not Mini tubbing or relocating the springs then
measure center to center of spring perch. And everything will still fit with the new rear. See B above
Also Dana’s have a longer snout (C) so you may need to shorten the driveshaft

If you plan to drive this car mostly in town go with 3.55 gears. If you drive a mix of highway and city driving go with 3.23 ratio.
Housing dimensions will be the tube length from the Dana 60 housing to the backing plates. The FSM gives these dimensions for your '72 Fury.
The perch location is for the spring mounts.

If you tell Strange the rear end is going into a "72 Fury, they should already have all those dimensions on file. They are listed on the post above.

If you plan to drive this car mostly in town go with 3.55 gears. If you drive a mix of highway and city driving go with 3.23 ratio.
Housing dimensions will be the tube length from the Dana 60 housing to the backing plates. The FSM gives these dimensions for your '72 Fury.
The perch location is for the spring mounts.

If you tell Strange the rear end is going into a "72 Fury, they should already have all those dimensions on file. They are listed on the post above.

Dave

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Dave,

I gave them that it was going into a 72 Fury, and they responded with the perch and housing question. That is why I got a little confused. I told them it would be stock leaf springs. Thanks Bud, I appreciate the combined wisdom.

Tire diameter must also be taken into account for knowing RPM on the highway.
Torque converter must be considered when choosing cam choice, and gear ratio considered for that.

Between 3.55 and 3.23 it really depends on where you plan to drive it more than anything. If you think you'll do 1-2 highway trips per year, 3.23 might 'feel' better at that particular time. If those trips will be 2hrs in length and rest of time is in-town, don't fret and go with 3.55. Most engine wear occurs at startup

Do NOT simply give Strange the measurements on that chart, measure your car for sure. When I put the slightly-narrower 8-3/4 B-body rear under my 68, my buddy and I went thru a bunch of housings (he had about 25 of them laying around) and it was very difficult to measure some of them and figure out what they were by that chart. Even then, we found some had 1/4" variation on spring perch locations and/or width when compared to axles that were otherwise the same. This blew my mind, as these things should've been jig-welded for assembly-line installation. I never would've believed it if I hadn't experienced it. I was trying to fit 8" Ramcharger wheels with 4" BS, so I needed a particular rearend, and we put a few in there until we found the best fit.

Which brings next point - axle width will depend on wheel choice, and perch location depends on where your springs are, and spring location determines tire choices. so if you're planning some fatties, you have to figure all of that out first.

8.75 rear axle with 3.55 ratio with an automatic transmission. You may need a Dana 60 or custom 9” with a 4 speed. Pinion snubber. Even the Hemis with automatics used a 8.75 rear axle.

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I agree, I would like a 8.75, but I am having a difficult time sourcing a complete rear end, then I would have the rebbuilt costs added to cost of the used rear end. If there is a readily available source of the 47.30 inch perch width axles out there, I certainly would consider the 8.75. Thanks,

I agree, I would like a 8.75, but I am having a difficult time sourcing a complete rear end, then I would have the rebbuilt costs added to cost of the used rear end. If there is a readily available source of the 47.30 inch perch width axles out there, I certainly would consider the 8.75. Thanks,

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All of the big block '73 Mopar C Bodies had 8.75 rear axles to start with (standard equipment), I would check my local wrecking yard for a complete unit. Most will already have either a 3.23 or 3.55 ratio.

@cbodybob , that chart in very limited , there are more different widths between years , just saying . check before choosing . and car weight , tire size , trans , engine performance , what you do , and want , and need from your car with make the gearing choice .

I agree, I would like a 8.75, but I am having a difficult time sourcing a complete rear end, then I would have the rebbuilt costs added to cost of the used rear end. If there is a readily available source of the 47.30 inch perch width axles out there, I certainly would consider the 8.75. Thanks,

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Check with Moser Engeneering. They sell a fabricated 8.75 called the MO875. Like Burger King you can have it your way. Call them up & tell them your specs. They build to suit. 2 weeks I believe. All 8.75 centers will work. There is even an aluminum center section 489 style if you have deep pockets. Cheaper than that Dana you are looking at.

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Check with Moser Engeneering. They sell a fabricated 8.75 called the MO875. Like Burger King you can have it your way. Call them up & tell them your specs. They build to suit. 2 weeks I believe. All 8.75 centers will work. There is even an aluminum center section 489 style if you have deep pockets. Cheaper than that Dana you are looking at.

I agree, I would like a 8.75, but I am having a difficult time sourcing a complete rear end, then I would have the rebbuilt costs added to cost of the used rear end. If there is a readily available source of the 47.30 inch perch width axles out there, I certainly would consider the 8.75. Thanks,

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Are you planning some 'capable' tires for behind the 505? If much wider than 255mm, your axle/springs/wheel backspacing becomes more important.

All of the big block '73 Mopar C Bodies had 8.75 rear axles to start with (standard equipment), I would check my local wrecking yard for a complete unit. Most will already have either a 3.23 or 3.55 ratio.

Dave

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Gotta disagree there, most will have 2.76, a smattering of 3.23, and I seriously doubt you'll find 3.55 in a C-body (from factory). Oh, maybe in a 6cyl-3spd Slabside car, but those would be the 'smaller' 741 housings and perhaps a poor choice for a 505's partner.

Are you planning some 'capable' tires for behind the 505? If much wider than 255mm, your axle/springs/wheel backspacing becomes more important.

Gotta disagree there, most will have 2.76, a smattering of 3.23, and I seriously doubt you'll find 3.55 in a C-body (from factory). Oh, maybe in a 6cyl-3spd Slabside car, but those would be the 'smaller' 741 housings and perhaps a poor choice for a 505's partner.

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I would agree that 2.76 ratios probably were more common than the 3.23 going from '73 onward. Still many of the pre '73 units were 3.23 and all of those 3rd members are interchangeable from one year to another once into the era past keyed axles. The 3.55 ratio's were mostly in either wagons or cars ordered with the trailer package option.

@cbodybob , that chart in very limited , there are more different widths between years , just saying . check before choosing . and car weight , tire size , trans , engine performance , what you do , and want , and need from your car with make the gearing choice .

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Yea I don’t like the chart either. I just wanted him to see the measuring points.